This invention relates to pneumatic/hydraulic power tools, and more particularly to a pressurized fluid driven power feed apparatus for concentrically applying thrust forces to an output shaft of a tool in a manner which distributes the thrust forces evenly concentrically about the output shaft.
In aircraft assembly operations, it is often necessity to clamp or otherwise attach a hand operated drill style reamer onto a spar or other area of a workpiece so that the reamer can be automatically operated. This has involved incorporating a pneumatic/hydraulic cylinder attached to some form of carriage, which is in turn coupled to the power tool that is performing the machining operation, whether it be drilling, cutting or reaming. As such, the pneumatic/hydraulic cylinder is laterally offset from the power tool.
The problem that arises is one of keeping the rotating working element attached to the output shaft of the tool perpendicular to the pneumatic cylinder. Put differently, the output shaft has to be maintained parallel to the cylinder and normal to the surface of the workpiece. Typically, guide rails or some other form of guide structure are attached to the tool in an attempt to keep the output shaft of the tool perfectly parallel to the cylinder and normal to the workpiece surface. These normality problems become less of a problem in larger tools as larger carriage bearings or guide rails are normally used. However, with smaller tools, the moment that is produced due to the high thrust loads and the distance between the component secured to the output shaft of the tool, such as a cutter, and the cylinder providing the thrust force causes the cutter to twist, thus pushing the cutter out of its alignment parallel to the surface of the workpiece. In a reaming operation, this can cause the cutter to exceed a predetermined hole tolerance for holes being formed in the workpiece.
The guide rail system presently used to align and support power tools also requires exacting tolerances which are quite difficult to maintain. Up until the present time, this problem of maintaining the correct angularity of the tool relative to the pneumatic/hydraulic cylinder has required the use of larger bushings and/or guides, which causes the overall assembly to become much more cumbersome to handle and set up and to require much more space.
It would therefore be highly desirable to provide some form of apparatus which can be used to support a tool and to provide thrust forces evenly (i.e., concentrically) about the output shaft of the tool as the output shaft is guided toward a workpiece. This would eliminate the need for large, heavy and cumbersome guide rail systems and/or carriages and would ensure that the thrust forces acting on the output shaft are applied evenly about the output shaft, and thus also evenly about the working element attached to the output shaft. Such an apparatus would also provide a more compact means for supporting the tool and its working element.
The present invention is directed to a power feed apparatus for feeding a working element attached to an output shaft of a motor driven power tool in a linear motion relative to a workpiece. The present invention enables a thrust force to be applied evenly about a periphery of the output shaft, and thus evenly about the working element, to ensure that the working element remains parallel to a surface of the workpiece as the thrust force is applied.
In one preferred form, the apparatus comprises a first tubular member which is adapted to be fixed to a substructure associated with a workpiece such as a jig, carriage or other like structure. A second tubular member is provided and moves slidably relative to the first tubular member. The second tubular member supports the tool thereon and allows the output shaft of the tool to extend therethrough into the first tubular member. The first tubular member includes a first annular fluid chamber arranged concentrically around the output shaft. The second tubular member similarly includes a second annular fluid chamber formed concentrically with the output shaft. The first tubular member further includes a bore at one end for enabling the output shaft of the tool to extend therethrough and toward and/or into a workpiece.
In operation, when a pressurized fluid is injected into the first annular fluid chamber, this causes the second tubular member to move slidably linearly relative to the first tubular member. This causes the output shaft of the tool to be moved linearly from a retracted position into an extended position wherein the working element attached to the output shaft can be used to perform a machining operation, such as reaming, for example, on the workpiece. When the working element is to be retracted, a pressurized fluid is removed from the first annular fluid chamber and injected into the second annular fluid chamber. This causes the second tubular member to be moved slidably in an opposite direction such that the output shaft is retracted, thus withdrawing the working element from the workpiece.
In a preferred embodiment the first tubular member further includes a biasing member such as a coil spring for assisting in retracting the output shaft. The biasing member is disposed within a biasing member retaining tube disposed fixedly relative to the first tubular sleeve and concentrically therewith such that it is able to receive the output shaft therethrough.
The power feed apparatus of the present invention thus allows a pneumatic or hydraulic thrust force to be applied evenly and concentrically about an output shaft of the power tool. This allows the output shaft to be driven in a smooth, linear motion without creating any external forces which would tend to act on the working element to force it out of its perfectly parallel alignment with a work surface. Advantageously, the power feed apparatus of the present invention also forms a very compact assembly which can be secured readily to a jig or other supporting structure associated with the workpiece.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limited the scope of the invention.